The present invention refers to electromagnetically operated miniature valves and in particular to a solenoid valve assembly of the type comprising a valve unit and an interchangeable solenoid having a core member and an axially slidable plunger housed in a protective tube protruding into an electromagnetic coil, said valve unit comprising inlet and outlet ports opening into a valve chamber, and a valve member provided in said valve chamber, said plunger of the solenoid acting on said valve member in opposition to a biasing spring to reciprocate said valve member in said valve chamber at the activation and deactivation of the solenoid to open and respectively to close said inlet ports; and disengageable locking means to connect said solenoid to said valve unit.
Valve assemblies of the above type are commercially available and are used in particular in automation systems using compressed air or for controlling the flow of liquids or gases, in which the valve unit usually operates as an interface member between an electronic control unit and a pneumatic or hydraulic device to be controlled, by changing, for example, an electric signal into a hydraulic or pneumatic flow or signal of a set value and time. Said solenoid valve assemblies are known for example from EP-A-0139811, FR-A-2603970 and US-A-4643393.
The solenoid valve assemblies of the above mentioned type are somewhat complex in the structure in that they require a valve unit having a body cast or molded in a single piece of metal or plastic materials, suitably worked to provide inlet and outlet ports and ducts necessary for fluid circulation, as well as the necessary internal components of the valve. In most cases (US-A-4643393 and FR-A-2603970) the valve body is also permanently joined to the solenoid or electromagnetic control unit; this precludes any practical possibility of inspecting the valve and flow paths after the solenoid and valve assembly has been assembled or mounted. All this results in structurally complex valve assembly having high production costs, and with restricted use in that materials capable of withstanding aggressive or high-temperature fluids cannot be used.
From EP-A-0139811 it is also know a miniature solenoid valve assembly having a valve unit and an interchangeable solenoid connected to the valve body by fixing pins passing through the valve body and the solenoid bodies; according to said miniature valve assembly, the valve body and the solenoid may be assembled and disassembled by inserting fixing pins or pulling them out of associates holes in said solenoid and valve body. Furthermore the valve body is cast or molded in a single piece preventing the use of plastic material to resist to gases and corrosive fluids. The valve body is provided with an open cavity for receiving one end of the solenoid, said cavity being in communication with a valve chamber through apertures in the bottom wall of said cavity for the passage of a fork projection of the slidable plunger acting on the valve member in the chamber. Therefore, according to said embodiments, no means have been provided for preventing the leakage of the fluid from the valve, as well as the loss of the sliding plunger in the disassembled condition of the solenoid. The manually operable fixing pins sometime are difficult to remove or to rotate when a small space is provided around the solenoid valve assembly in an assembled and working condition.
With the foregoing problems in view, the present invention has the primary object to provide a miniature solenoid valve assembly in which the solenoid may be simply engaged and disengaged by the valve unit by simply pulling and pushing it, in which the solenoid may be disengaged preventing leakage of fluid from the valve unit and the loss of components the disengaged condition of said valve unit and solenoid units.
A further object of present invention is to provide a solenoid valve assembly as stated above comprising a valve unit of simple design allowing an inspection of the components and withstanding to corrosive fluids while maintaining a comparative low cost.